1. Field of the Invention
The invention relates to a device for biological fluid treatment, i.e., waste water treatment, in which a fluid to be treated is led along surfaces coated with microorganisms.
2. Description of the Prior Art
Biological cleaning stages which function aerobically or anaerobically are applied in particular when treating waste-water. With this it is the case of so-called substrate biologies, i.e. of microorganisms with are fixed on a substrate material with a large surface, along which the fluid to be treated is led. Such a method is known for example from EP 0 470 931 A2.
One problem with this surface coated with microorganisms is the fact that the surface activity changes with a growing layer thickness, since with an increasing layer thickness, the microorganisms lying at the bottom are more poorly supplied, and thus may not take part so actively in the process. The excess microorganisms therefore need to be removed from the surfaces at regular intervals and the sludge which settles from this needs to be led away, which is usually effected by back-rinsing or by way of a scraper. Such scraper devices are known for example from GB 1418348 A and DE 44 41 866 A1.
A further problem with closed reactors with which the fluid is led in channels and with which the mostly filigree channel walling serves as adhering surfaces for the microorganisms lies in the fact that the channels clog with an increasing layer thickness of the microorganisms, and a through-flow occurs only with an increased resistance, by which means the activity likewise reduces. In contrast to this, with open reactors as for example are known from U.S. Pat. No. 3,466,241 A1 or U.S. Pat. No. 4,157,303 A1, the fluid flow is led past stacks of disks which form a comparatively large surface for carrying the microorganisms, which however are comparatively poorly used due to the fact that the disks are only partly immersed in the waste-water.